Field of the Invention
The present invention relates to the treatment of scoliosis, and, in particular, to implant devices and methods for treating scoliosis.
Description of the Related Art
Treatment of scoliosis, which is a spinal deformity resulting in an abnormal curvature of the spine, can range from halo traction devices that severely limit the movement of the patient, to rod-based and interbody systems that are inserted along the spine. Both of these exemplary methods can be extremely traumatic to the patient.
Surgical attempts to correct curvatures of the spine were first attempted in the mid to late 19th century by using percutaneous myotomies of the vertebral musculature in addition to bracing. Further developments in the surgical aspects of correcting scoliosis were not realized until the early 1900s, but the development of external casts and braces continued throughout the late nineteenth century. For example, Plaster of Paris casts in 1880 were applied to patients while standing in vertical suspension devices. The bracing method tried to correct the deformity in both lateral and rotational methods and held them with a cast. Horizontal distraction frames utilized cast application to create a three-point fixation.
Later, postoperative immobilization such as the localizer cast, which consisted of a specialized frame where pressure was applied to the rib cage, was used. This allowed correction to be obtained immediately after surgery and also allowed for patients to be ambulatory after the operation. A Milwaukee brace was used initially as a postoperative immobilization device as well as a non-operative treatment of the disorder.
Further techniques used Harrington distraction instrumentation, which straightened the spine while holding the spinal column rigid while fusion took place. This included a steel rod on a ratchet system attached to the spine with hooks at the top and bottom of the curvature that would distract the curve when cranked. A segmental instrumentation system used crosslinking of two rods in the back to provide three-dimensional correction of the scoliotic deformity and decrease the need for immobilization after the surgery.
Presently, surgical practice uses a combination of devices (rods, cables, interbody cages, screws, and hooks) to move the spine into a natural alignment and keep it in that alignment until the bone graft fuses into place. These procedures generally link multiple vertebral bodies by attaching polyaxial screws or hooks to the spine and placing a rigid rod in place to link the spinal column. These procedures are completed with either an interbody fusion techniques or by leaving the native intervertebral disc intact.
However, hardware failure and non-fusion rates of 70% of patients receiving rod and screw fixation for multiple level deformity correction have been reported. The high degree of hardware failure suggests that alternative methods should be developed to both correct scoliosis deformity and minimize the reoperation rates.
Another alternative surgical method presently available approaches the lateral aspect of the spinal column through a lateral approach. Lateral interbody fusion has recently become attractive and a less invasive alternative to full posterior rod and screw fixation. The lateral procedure generally involves creating a lateral incision in the thoracolumbar spine, removing one or multiple intervertebral discs, and placing an intervertebral interbody spacer in place of the disc. The intervertebral interbodies are designed to realign the spine by including a built-in lordotic angle into the interbody. This procedure is commonly used in conjunction with lateral plating or in some instance posterior fixation with screws and rod fixation.
One major limitation with the interbody fusion technique is a surgeon's ability to correct only one plane of correction. Spinal scoliosis often involves multiple planes of deformity and requires correction of both sagittal alignment and coronal planes. The current interbody techniques on the market are only able to gain this correction in one plane and require additional alignment correction.
It would be beneficial to provide an implant that can be tailored to a single vertebra based on the particular physical needs of individual patients.